This change means that plugin authors can now use newer PHP syntax in plugins they submit to the official plugin directory. In the future, the version maximum will match what’s running on WordPress.org.
PHP 7.3 was released on December 16, 2018, and PHP 7.4 will be released on November 28, 2019.
PHP 7.2 will lose active support on November 30, 2019, and security support on November 30, 2020.
“Given PHP’s poor adoption curves,”… “all that this means is that you can’t release a plugin through WordPress.org that only works on 15% of WordPress sites. “You can even use newer functions in PHP if including compat code, just not newer syntax.”